There are numerous systems utilizing light for signaling and information-portraying purposes.
For example, a panel having a painted or printed sign illuminated by lights disposed around or spaced from the panel, can be used for the display of information of various types, for signaling and for various public information purposes. In general, however, such systems have the drawback that the panel is single purpose and must be repainted or recovered for use to convey different information. Furthermore, the panel completely fills the space occupied thereby and obstructs the view behind the panel. Also the illuminating system must be developed as a unit separate from the panel.
There are displays which back-light a panel filling a field of view so that the informational message can be seen from a distance. While these displays incorporate the source of illumination in the panel itself, they nevertheless have the drawback that they are single purpose and not convenient to change and, of course, obstruct the field of view.
There is, of course, a full spectrum of displays between the panel-type displays described, moving-light displays which are of high versatility with respect to the message but are expensive and also can obstruct a field of view, and neon-sign and other open displays where alphanumeric characters are formed from neon tubes so that there is a minimum obstruction of the field behind the display.
Neon-tube displays, however, have the drawback that they are usually single purpose as well and require complex fabrication procedures. By and large, the cost of such displays is high and the esthetic results are poor.